1. Field of the Invention (Technical Field)
The present invention relates to cooling of electronic assemblies.
2. Background Art
With the introduction of integrated circuits (ICs), there has been a steady progression toward larger and more complicated IC devices to permit the inclusion of a greater number of functions on the IC. With larger ICs having more circuitry, more heat is produced that is not adequately removed by natural air convection alone nor by powered ventilation, such as a fan.
A heat sink is a device that preferably has a relatively high rate of thermal conductivity and high heat capacity. Because of the material properties of the heat sink and its design, a heat sink can draw heat from any closely situated heat source and dissipate that heat into the surrounding environment. The heat that is generated by ICs must be removed from the area of operation, or else the IC can be ruined.
Convection cooling is performed by the use of a heat sink that is directly applied to the device. It is not desirable to use a bonding process, such as an adhesive, because of the permanent nature of such attachment; an IC may be discarded if malfunctioning and it is not desirable to throw away the heat sink as well as the IC. It has therefore been found beneficial to attach a heat sink to the IC by mechanical means, such as a retainer clip. The typical heat sink in current use comprises a flat plate, generally of the same size as the device, with a plurality of radiation fins extending upwardly. The heat sink is commonly fabricated from aluminum and is extruded and subsequently machined.
A parallel development in the electronic assembly art has been the provision of means for detachably securing large and generally expensive IC devices to a printed circuit board. By detachably securing these expensive ICs, they can be easily removed and repaired when one part of the device becomes damaged or is inoperable. This eliminates the need for fixing the device while it is attached to the printed circuit board, removing the device with possible damage to the sensitive pins, or throwing away the entire IC and printed circuit board. Typically, the industry uses sockets for detachably securing ICs to printed circuit boards. Sockets are permanently attached to the printed circuit board through soldering of downwardly-extending contact pins. These sockets for semi-conductor devices are typically standardized for various ICs and/or IC families.
Recently, however, a new low-cost microprocessor module has been developed that will be used instead of a socket. The microprocessor module consists of the microprocessor IC that is soldered to a small printed circuit board, which is in turn detachably secured to the larger printed circuit board.
To facilitate the proper attachment of the heat sink to the microprocessor module and associated printed circuit board and microprocessor, the printed circuit board within the module is provided with holes that correspond to holes through the plate of the heat sink, through which a retainer clip is inserted. The retainer clip then secures the heat sink to the bottom of the printed circuit board, and at the same time secures the microprocessor module in tight engagement with the heat sink.
Heat sinks to be used with microprocessor modules and printed circuit boards may be of various constructions, but all heat sinks are fabricated or formed from a material with high thermal conductivity, such as aluminum. Heat sinks include a plate with a flat bottom surface. The plate is generally rectangular and its size is co-extensive with the size of the entire device, which includes the printed circuit board and microprocessor module. The heat sink has a large number of fins that are integral with the plate and formed from a single extrusion. In the central region of the heat sink, the fins are machined away to create a channel that extends across the plate.
The heat sink is retained on the entire device by a resilient retainer clip that biases the heat sink into tight thermally conductive relation to the device. That is, the lower surface of the plate is forced against the upper surface of the device.
Prior art heat sink and retainer clip devices are disclosed in U.S. Pat. No. 5,600,540 to Blomquist, entitled xe2x80x9cHeat Sink and Retainer for Electronic Integrated Circuits;xe2x80x9d U.S. Pat. No. 5,396,402 to Perugini, et al., entitled xe2x80x9cAppliance for Attaching Heat Sink to Pin Grid Array and Socket;xe2x80x9d and in U.S. Pat. No. 5,208,731 entitled xe2x80x9cHeat Dissipating Assembly.xe2x80x9d U.S. Pat. No. 5,208,731 discloses an assembly for heat dissipation using a spring clip which cooperates with tabs or lugs on opposite side walls of a socket to retain a microprocessor or other IC. U.S. Pat. No. 5,396,402 discloses the use of a clip, which includes a leaf spring and two plastic clips, to be used specifically with a pin grid array chip and pin grid array socket. U.S. Pat. No. 5,600,540 discloses a heat sink and retainer clip to be used with a rectangular socket having opposing side walls, wherein at least two of the side walls have lugs projecting laterally outward. That particular retainer clip is constructed in two pieces; one of which is an elongated strap having a bent portion that bears down upon the heat sink, and another that is rotatably mounted on the end of the first which, when forced down and rotated inward, hooks an opening onto a lug. These prior art devices are made differently and operate differently from the present invention.
The present invention is a simple design to be used with microprocessor modules or any electronic device to be retained against a heat sink, and has the added benefit of producing an evenly-distributed load across the printed circuit board, and microprocessor, during and after installation. The present invention has a flexible slotted rail and pin configuration and a handle for the user to pull back and forth to install and remove the clip.
The present invention is a heat sink retainer clip for biasing an electronic device mounted on a printed circuit board within a housing and a heat sink into heat transfer engagement. The clip comprises at least one rail supported on the housing; at least one pin to be inserted through registered openings in the heat sink, printed circuit board, and housing; a slot in at least one of the rails for receiving the pin; and a handle for positioning the clip relative to the heat sink, printed circuit board, and housing from a first relaxed position to a second biasing position. The pin or pins of the clip preferably comprise a body, a base at one end of the body to abut the heat sink, a spacer at the middle of the body to maintain an approximate fixed distance between the electronic device and the heat sink, and a bulb at the opposite end of the base of the body extending through the slot in the rail to abut the slot when the clip is in the biasing position. Preferably, each pin is comprised of thermoplastic. Preferably, the handle is connected between two corresponding ends of the rails. The rails have at least one arched portion which produces a biasing force and at least one flat portion connected to the arched portion that is in contact with the housing. Preferably, the arched portion produces a biasing force of between approximately 10-20 pounds. The slot in the rail preferably has a registered hole for initially receiving the pin. Preferably, the slot is located so that the end of the slot opposite the registered hole is located at the highest point of the arched portion. The clip is preferably made of resilient stamped metal.
In a preferred embodiment, the heat sink retainer clip is comprised of two rails supported on the housing; four pins to be inserted through registered openings in the heat sink, printed circuit board, and housing; four slots in the two rails which receive the four pins; four holes through the two rails, and adjacent to the four slots, corresponding to the four pins to initially receive the pins; and a handle for positioning the clip relative to the heat sink, printed circuit board, and housing from a first relaxed position to a second biasing position. In this embodiment, the clip further comprises at least one transverse rail connected between the two rails for additional stability. Each of the four pins comprises a body, a base at one end of the body to abut the heat sink, a spacer at the middle of the body to maintain a fixed distance between the electronic device and heat sink, and a bulb at the opposite end of the base of the body to abut the slot when the clip is in the biasing position. Preferably, the four pins are made of thermoplastic. Preferably, the handle is located transverse to the two rails and is used to expand and contract the two rails concurrently into relaxed and biasing positions, respectively. Each of the two rails preferably comprise two arched portions for producing a biasing force directed away from the electronic device, and at least one flat portion adjacent the arched portions for producing a biasing force down upon the electronic device. Preferably, each of the slots is located along one of each of the arched portions, and each of the holes is in communication with and adjacent to a corresponding one of the slots and located upon the flat portions. Preferably, the slots are located so that the end of each slot opposite the hole is located at the highest point of the arched portion. The clip is preferably comprised of resilient stamped metal.
A method of attaching the heat sink to the electronic device is comprised of the steps of inserting at least one pin through corresponding holes in the heat sink and electronic device; aligning the corresponding holes in the retainer clip to the pins; positioning the retainer clip holes over the pins and onto the electronic device; expanding the retainer clip and concurrently sliding the pins through the slots upon the retainer clip; and providing an upward force upon the pins to pull the heat sink into tight engagement with the electronic device while concurrently providing a downward force upon the electronic device by the retainer clip.
The heat sink retainer clip can be used with the heat sink having a base and a plurality of fins, a printed circuit board on which is mounted an electronic device, such as a microprocessor, and a module housing for the printed circuit board. This heat sink retainer clip can comprise at least one rail of resilient material having an elongated slot, and includes at least one flat portion positioned upon an exterior wall of the housing, and at least one arched portion, wherein the elongated slot extends from the flat portion to the arched portion; and at least one pin having a base at one end and a bulb on the other end which passes through registered holes in the heat sink, printed circuit board, and the module housing, such that when the rail is in a first position the bulb protrudes through the flat portion of the elongated slot in the rail, and when moved to a second position where the bulb protrudes through the arched portion of the elongated slot in the rail, the pin base and bulb are biased so as to force the heat sink into heat transfer engagement with the electronic device. This clip can additionally comprise at least one additional rail with an elongated slot, means for attaching the rails in longitudinal alignment, and at least one additional pin passing through registered holes in the heat sink, printed circuit board, and the module housing, so as to provide additional biasing force to the heat sink and electronic device. These elongated slots are bayonet slots, the clip is preferably formed from stainless steel, and the pin is preferably made of plastic.
A primary object of the present invention is to provide a heat sink retainer clip that applies uniform pressure across a printed circuit board, microprocessor, and microprocessor module during and after installation.
Another object of the present invention is to provide a heat sink retainer clip that has a minimum number of working parts, presses easily into place upon the printed circuit board, and retains the heat sink by simply pulling a lever to lock into place.
A primary advantage of the present invention is that no alignment fixtures are necessary to install the retainer clip.
Another advantage is that it can be adapted to fit a variety of heat sinks, printed circuit boards and associated modules.
Other objects, advantages and novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.